Coated fabric and method of application



Patented Aug. 8, 1944 COATED FABRIC AND METHOD'OF APPLICATION Benjamin Raymond Hanson, Dayton, Ohio, as-

signor to The Sherwin-Williams Company, a

corporation of phio No Drawing. Application June 18, 1940.

Serial Isa-351,149

8 Claims. ((1117 66) This invention relates to the covering of structures with a coated fabric, and involves an improved method as well as'improvements in the coated fabric to be applied.

The invention is particularly applicable to such structures as airplane wings, where the fabric employed must be in a smooth, taut condition and substantially impervious to water and air.

Heretofore it has been proposed to pretreat textile material by the application of a solution and the fabric will be smooth and will perfectly follow such curves when the drying is completed after the application of the fabric.

By means of my invention the fabric in its final dried condition will have the form desired, will closely follow the contour of the structure to which it is applied, and there is comparatively shrinks and produces the smooth, taut surface.

It has also been proposed to apply untreated textile material such 'as light weight cotton, and coat it while in place, so that upon the evaporation of the solvent the fabric becomes taut.

In both such procedures it is necessary to do some of the treating of the fabric after it has been applied to the structure.

The main objects of the present invention are to simplify the procedure, to reduce the time required for shrinking the fabric after its application to the structure, and to avoid the necessity for the. application of any liquids to the fabric after it is secured in place on the airplane wing or other structure.

In carrying out my invention I employ a fab-. ric which has been pretreated with a solution of the film forming material, but which still contains aconsiderable amount of the solvent. The

- amount of the solvent is not so small as to make the fabric harsh or stiff, and is not so large as to make it tacky. l

The film forming composition is thus in a swelled condition in the fabric, but at the same time itv is'in a sufilciently dry condition so that the fabric is handleable and in soft pliable con-..

dition. The film andfabric retainv sufficient solvent to maintain the gel structure of the body portion of the film in a swelled condition, and thus when the fabric is applied to thestructure and the remaining solvent evaporates, the volume of the coating decreases, the fabric shrinks,

and there is produced the propertautness'jand the fabric is tightly and smoothly applied.

.As the fabric and the film are in soft condition at the time the fabric is applied, it may be worked over and around complicated curves,

commonly called dope small loss of solvent, as the major portion of the solvent originally used is evaporated at the factory where the fabric is prepared, and where the evaporated portion may be readily recovered.

Where untreated fabric is first secured to tlie structure and the coating is applied thereafter, the operation requires considerable skill and dif: flculty in the application of the coating, and there is a large loss of solvent mixture. If the film is thoroughly dried on the fabric before the latter is applied to the structure, the original gelled condition cannot be readily restored by the mere application of solvent while the fabric is inplace. Even when such solvent is applied there is obtained only a, relatively small percentage of .the original tautening power, whereas the bulk of the tautening power is available when employing my invention.

I do not claim any special novelty in the ingredients employed in the coating composition. The film forming material may be cellulose esters such as cellulose acetate, or may be a nitrocellulose or a suitable cellulose ether.

' ingredients, and therefore no definite percentage of retained solvent can be fixed which will be applicable to all coating compositions which may be used.

The compositions employed in the treatment of fabrics for airplane wing constructions are As an example, a fabric maybe finished at the factory in the conventional manner, using three spray coats of clear dope, one of aluminized clear, and three of pigmented dope. The specific gravity of-the film may be about .909 and the specific gravity of the retained solventabout .361. A suitable solvent mixture may have the following formula:

. Gallons Amyl acetate -L.

with such a compo'smn the upper limit of by weight of the dried film may be between about The best working range 40% and about for such ethyl cellulose dope appears to lie between and 35% of the absorbed volatile. For light weight cotton airplane fabric, the optimum working range is between 15% and 30%.

while for the same finish on glass fabric the range is from to 35%. The difference may be due to the great difficulty of tautening doped glass fabric. The actual dissolving strength of the volatiles already within the film also affects the results obtained. A low molecular weight solvent such as ethyl acetate, for instance, will produce a given degree of softening with a lower percentage of volatile in the film than will a high molecular weight solvent such as amyl acetate.

The fabric pretreated at the factory may be put in sealed containers in roll form, or in the form of pieces cut to the proper size and shape to constitute the complete assembly for an airplane wing. The solvent is prevented from evaporating by the sealing of the container, and preferably in the container is placed an absorbent containing solvent so as to maintain the concentration of vapors in the container in equilibrium with that contained in the film. Thus the precoated fabric may be maintained in proper condition for use at any time desired; If desired, the absorbent containing the ,solvent in the container may be in a separate compartment from that containing the fabric, but in open communication therewith.

It is preferable to employ a high percentage of high boiling solvents such as amyl or ethyl acetate and non-solvents such as xylol or Solvesso #2, in the composition applied to the fabric, so thatthe solvent will not evaporate too quickly after the container is opened, and so that adequate time will be available for the securing of the fabric in place on the wing structure.

So far as the process is concerned, one can either ship the fabric in a sealed container with the proper solvent content, or it may be shipped in a somewhat drier condition and then put in a, cabinet containing solvent vapors to soften it up to the required extent before securing the fabric in place.

film soft, but insufliclent to render it tacky,

.whereupon the fabric becomes taut upon further evaporation'of the solvent and the reduction in volume of the coating.

2. A process of forming a structure having a coated fabric covering in taut condition, which includes securing to the structure a fabric having a soft film of coating composition retaining insufficient solvent to render it tacky, and permitting the evaporation of the remaining solvent after the application of the fabric to the structure, whereby the fabric becomes taut durin the'evaporation of the remaining solvent.

3-. The process of forming a taut, smooth covering on a rigid structure such as an airplane wing, which includes coating a cloth with an ethyl cellulose dope, evaporating a portion of the solvent thereof to leave between 10% and 40% of the volatile ingredients, and to make the coating nontacky, and securing the cloth in this condition to the rigid structure, whereupon the further evaporation of solvent reduces the volume of the coating, shrinks the cloth and renders the covering taut and smooth.

.4. Soft, flexible material for .use in forming a taut covering on a structure after being secured thereto and exposed to permit evaporating action, said sheet material comprising a sheet of cloth having a soft non-tacky coating containing a film forming oellulosic substance, 9. volatilesolvent and a volatile non-solvent which is miscible therewith, said volatile solvent being present in insufficient amount to render the coating tacky,

. securing of said sheet to said structure.

claim as new and desire to secure by Letters Patent is:

1. The process of forming a taut fabric cover/ ing on a rigid structure, which includes coatin the fabric with a composition including a film forming material and a solvent, evaporating off 5. As an article of manufacture for use in forming a taut covering on a structure after being secured thereto and exposed to permit evaporating action, a soft, flexible sheet of cloth having a soft non-tacky covering containing a cellulosic film forming material, and a solvent mixture including a volatile solvent for said material, and a volatile non-solvent miscible with said volatile solvent, said solvent mixture constituting between 35% and 75% of the weight of said material, said volatile non-solvent retarding but not preventing evaporation of said volatile solvent, said volatile solvent being present in insufiicient amount to render the coating tacky, but in sufficient amount 'to retain said coating in soft condition and to permit stretching of the sheet, said film forming material causing shrinking of said sheet upon the evaporation of said volatile solvent after the securing of said sheet to said structure.

6. As a new article of manufacture, a sheet composed of cloth having a soft non-tacky coating containing a film forming cellulosic material and a solvent mixture including a volatile nonsolvent and a volatile solvent, said solvent mix- 'ture being present in sufficient amount to maintain said coating in soft condition, and in insuflic1en t amount to render said coating tacky, and an impervious casing enclosing said sheet and preventing escape of said solvent mixture, and

thereby preventing hardening of said coating and shrinking of said sheet during shipment and storage, and said volatile non-solvent being in suflicient amount to retard but not prevent evaporationof said volatile solvent after removal of said casing, whereby said sheet may be secured to a structure and thereafter shrink and its coating harden during evaporation of said solvent mixture.

'7. As a new. article of manufacture, a sheet composed of cloth having a soft non-tacky coating containing a film. forming material and a solvent mixture including a volatile non-solvent and a volatile solvent, said volatile solvent being presentfin suflicient amount to maintain said coating in soft condition, and in insuflicient amount to render said coating tacky, an impervious casing enclosing said sheet and preventing t escape of said solvent mixture from proximity to said sheet, and a solvent-containing absorbent also enclosed in said casing to maintain substantially constant the concentration \of vapors of said solvent mixture in said casing.

'8. The process of preparing an article suitable for later use in making a taut, smooth covering on a rigid structure such as an airplane win which includes coating a fabric with a cellulosic composition in a volatile solvent, evaporating a portion of. the solvent to leave between 10% and 40% of the volatile ingredients, and to make the coating soft and non-tacky, and sealing the fabric with the coating in that condition in an impervious casing, to substantially prevent further evaporation of solvent from the coating during storage and prior to the securing of the fabric on said rigid structure.

BENJAMIN RAYMOND HANSON. 

